The panels of this invention are relatively light in weight having layers of foamed plastic material rather than heavier materials such as fiberboard, particle board or hardboard, etc., for example.
In the past, lightweight panels having a relatively soft, foam-backed and/or expanded vinyl foam-in-place cover sheet on a relatively hard, self-supporting core have been made by methods requiring several steps. One such method involves providing a soft, open cell core-forming foam layer impregnated with a heat-activatable hardening solution, and a soft, open cell barrier foam layer. An assembly including both of these foam layers is built up, consisting of a thermoplastic film, the barrier foam layer, the impregnated core-forming foam layer with glass fiber rovings on both sides, a second thermoplastic film and a scrim sheet. This assembly is passed between unheated nip rolls to squeeze some of the solution from the core-forming foam layer into the barrier foam layer with the solution trapped between the two thermoplastic films. Separately, a soft, open cell foam-backed cover sheet is made by securing a foam backing to a cover sheet. Some of the methods used are a film bond, spray-on adhesive, flame laminating, or an adhesive powder coating, for example. Alternatively, a cover sheet without foam backing may be provided. Then in a final step, the cover sheet is placed over the barrier foam layer (with the thermoplastic film over the barrier foam layer still in place or not as desired) and the assembly is subjected to heat and pressure between contoured dies in a compression molding operation to produce a finished panel. During the molding operation, some of the hardening solution may (depending on whether or not the thermoplastic film is left in) transmit to the foam backing of the cover sheet. The hardening solution is activated and hardens the core-forming layer and the barrier layer and to a lesser extent the foam backing. All of the parts of the panel are secured together in the molding operation by the heat-activated catalytic solution and by the melted thermoplastic film. U.S. Pat. No. 4,451,310 generally describes portions of this method.
We have developed an improved lightweight panel having a relatively soft foam-backed cover sheet supported on a relatively hard, self-supporting core,.and a method of making the panel in one simple step. An assembly of foam layers is built up comprising a core-forming foam layer, an intermediate foam layer, and a cover-backing foam layer, with a scrim sheet under the core-forming foam layer and a cover sheet over the cover-backing foam layer. Adhesive films as well as reinforcing fibers between layers may also be provided. The core-forming layer is impregnated with a heat-activatable hardening compound coating the cell walls of the foam. The intermediate layer and the cover-backing layer may also, if desired, be impregnated with a heat-activatable hardening compound but usually in lesser amounts.
The panel is formed by subjecting this layered assembly to heat and pressure between contoured dies in a single compression molding operation at a temperature at which the hardening compound is activated. The layers of the assembly are bonded together either by the hardening compound or by thermoplastic films placed between layers which are melted by the heat of the molding operation and become adhesive when melted, or both.
In the molded panel, the core or base layer becomes relatively hard and self-supporting, the cover-backing is relatively soft and compressible to the touch, and the intermediate layer is not as hard as the core-forming layer but not as soft as the cover-backing layer. The relative softness or hardness of the layers will vary depending upon the amount of hardening compound with which they are impregnated. Other factors affecting softness or hardness are the thickness, density and compression of the foam layers, and the concentration of the hardening compound. The concentration of the hardening compound may be reduced by means of a solvent.
A panel may also be formed according to this invention consisting essentially only of a foam-backed cover sheet on a preformed, self-supporting core.
These and other objects of the invention will become more apparent as the following description proceeds, especially when considered with the accompanying drawings.